1. Field of the Invention
The present invention relates to an information recording/reproduction apparatus that records or reproduces image pickup information, or the like, onto or from a disk-shaped recording medium, such as a CD, a DVD, an MD, or a Blu-ray Disc.
2. Related Background Art
In recent years, recording/reproduction apparatuses that are capable of recording/reproducing not only audio signals, but also, video signals, whose information amounts are larger than those of the audio signals, have come into widespread use, as a result of an increase in recording densities of disk-shaped recording media. For instance, video camera apparatuses containing disk-type recording media (hereafter referred to as “disk camcorders”), such as camcorders using DVDs, have been developed and mass produced. Means for preventing degradation of recorded information due to vibration of a recording/reproduction apparatus using a disk-shaped recording medium in such a disk camcorder is proposed in Japanese Patent Application Laid-Open No. 2004-158149, for instance. This patent document will be described below.
In general, in a recording/reproduction apparatus that records/reproduces information by irradiating laser light from an objective lens onto a disk-shaped recording medium, such as an optical disk, the information is recorded/reproduced through an intermittent operation, such as an operation shown in FIG. 4. That is, as distinct from the case of a tape medium onto/from which information is sequentially recorded/reproduced, in the case of a disk medium, there are a period “a”, in which information is actually recorded/reproduced onto/from the disk medium, and a period “b” in which no information is recorded/reproduced thereonto/therefrom.
When an image pickup time of image pickup information having the same data amount is referred to as “t(a+b)” and the data is recorded, for instance, a period required to record the data becomes “t” in the case of a tape medium, but becomes around one-third of “t” in the case of a disk medium, such as a DVD, under present circumstances. Note that, in FIG. 4, for ease of explanation, only an intermittent operation at the time of recording is shown, but the same intermittent operation is also performed at the time of reproduction.
In the case of the conventional example described above, there are the following problems. That is, in general, an objective lens that irradiates laser light onto an optical disk is mounted on an objective lens actuator. Also, the objective lens is constructed so that it is biaxially drivable to follow axial runout of a disk surface (deflections that occur in a direction vertical to the disk surface) and radial runout (deflections that occur in a direction parallel to the disk surface), and the actuator is driven.
The objective lens actuator is constructed by holding a movable portion to which the objective lens is fixed by four wires, and using a magnetic circuit formed by a coil disposed for the movable portion and a magnet disposed for a fixation portion. The objective lens actuator adopting the four-wire system is widely used, so the description of a concrete structure thereof will be omitted.
An operation to follow the axial runout described above and an operation to follow the radial runout described above are respectively referred to as the “focus (hereafter abbreviated as “Fo”)” and the “tracking (hereafter abbreviated as “Tr”)”, and information is recorded/reproduced by forming a spot on a recording surface of a disk and causing the spot to follow tracks arranged on the recording surface.
When a disturbance, such as vibration or shock, arises, however, a problem occurs that track following is lost, and a recording/reproduction operation becomes impossible. In order to solve this problem, image pickup information is accumulated in a semiconductor memory, and the recording/reproduction operation is performed again for the period “b” shown in FIG. 4, in which no information is recorded/reproduced. When the vibration, or the like, continues for a long period of time, exceeding the capacity of the semiconductor memory, the track following becomes impossible, and, thereby, the recording becomes impossible, or it becomes impossible to record information with the required precision. Alternatively, there occurs a problem (hereafter, referred to as “degradation of recorded information”) of writing information onto an unintended track adjacent to a track to be written and, thereby, accidentally overwriting data on the adjacent track.
In the aforementioned conventional technology, degradation of image pickup information due to vibration, such as camera shake, is described. However, the recorded information degradation problem, which occurs at the time of recording onto a disk medium due to the above-described situation, in which the track following becomes impossible (hereinafter, referred to as “servo instability”), is not described. That is, in an extreme example, there is a possibility that there will occur a problem in that even when image pickup information has been shaken due to vibration, such as camera shake, and “no image has been recorded” as a result of the servo instability described above, an operation recognizes that “an image has been picked up”.
Also, recent camcorders are each provided with an automatic focus adjustment function. With this function, when it is difficult to obtain an in-focus state with respect to a subject, for instance, a focus adjustment operation is repeated many times, and vibration occurs for a long time, which results in an occurrence of the servo instability.
Further, also when an operator uses zoom means repeatedly, there is a possibility that the same vibration will occur. Still further, as is also apparent from FIGS. 4 and 6 of Japanese Patent Application Laid-Open No. 2004-158149, in a recording/reproduction apparatus that uses a disk-shaped recording medium and performs recording/reproduction through an intermittent operation, even after image pickup by an operator has ended, recording of information is continued for awhile. Therefore, when the operator determines that the image pickup has ended and places the recording/reproduction apparatus on a desk, or the like, roughly, before the information recording is completed, large vibration, or the like, is given to the apparatus and the servo becomes unstable, which results in a possibility that an inconvenient situation, in which recorded information is lost or degraded, or the like, will occur.
It is considered that the problem particularly tends to occur to users accustomed to video camcorders that use tape media, that perform sequential recording during image pickup, and that stop the recording concurrently with the end of the image pickup. In the patent document described above, no countermeasure against this problem is discussed.
In addition, mobile devices, such as disk camcorders, are battery-driven, so there is also a demand for a reduction in power consumption. In the conventional technology described above, there is no specific description as to the power consumption. Also, as will be described in detail later, the case of an intermittent operation, in which information is recorded/reproduced through rotation at a high number of revolutions, makes it possible to reduce power consumption greatly, as compared with the case of rotation at a low number of revolutions.
When information is recorded/reproduced through the rotation at the high number of revolutions, the operation to follow the disk surface axial runout, and the operation to follow the radial runout, need to be performed at a high acceleration, as compared with the case of the low number of revolutions. Consequently, there is a problem in that, in the case of the high number of revolutions, a wide servo bandwidth is required, as compared with the case of the low number of revolutions and, therefore, the servo instability tends to occur, as compared with the case of a low speed.